The present invention relates to polishing pads for chemical mechanical polishing (CMP), and in particular relates to polymeric composite polishing pads suitable for polishing at least one of semiconductor, magnetic or optical substrates.
Semiconductor wafers having integrated circuits fabricated thereon must be polished to provide an ultra-smooth and flat surface that must vary in a given plane by less than a fraction of a micron. This polishing is usually accomplished in a chemical-mechanical polishing (CMP) operation. These “CMP” operations utilize chemically active slurry that is buffed against the wafer surface by a polishing pad. The combination of the chemically active slurry and polishing pad combine to polish or planarize a wafer surface.
One problem associated with the CMP operation is wafer scratching. Certain polishing pads can contain foreign materials that result in gouging or scratching of the wafer. For example, the foreign material can result in chatter marks in hard materials, such as TEOS dielectrics. For purposes of this specification, TEOS represents the hard glass-like dielectric formed from the decomposition of tetraethyloxysilicates. This damage to the dielectric can result in wafer defects and lower wafer yield. Another scratching issue associated with foreign materials is the damaging of nonferrous interconnects, such as copper interconnects. If the pad scratches too deep into the interconnect line, the resistance of the line increases to a point where the semiconductor will not function properly. In extreme cases, these foreign materials create macro-scratches that can result in the scrapping of an entire wafer.
Reinhardt et al., in U.S. Pat. No. 5,572,362, describe a polishing pad that replaces glass spheres with hollow polymeric microelements to create porosity within a polymeric matrix. The advantages of this design include uniform polishing, low defectivity and enhanced removal rate. The IC1000™ polishing pad design of Reinhardt et al. outperformed the earlier IC60 polishing pad for scratching by replacing the glass shell with a polymeric shell. In addition, Reinhardt et al. discovered an unexpected maintenance in planarization efficiency associated with replacing hard glass spheres with softer polymeric microspheres. The polishing pads of Reinhardt et al. have long served as the industry standard for CMP polishing and continue to serve an important role in advanced CMP applications.
Another set of problems associated with the CMP operation are pad-to-pad variability, such as density variation and within pad variation. To address these problems polishing pad manufacturers have relied upon careful casting techniques with controlled curing cycles. These efforts have concentrated on the macro-properties of the pad, but did not address the micro-polishing aspects associated with polishing pad materials.
There is an industry desire for polishing pads that provide an improved combination of planarization, removal rate and scratching. In addition, there remains a demand for a polishing pad that provides these properties in a polishing pad with less pad-to-pad variability.